docs: def convert_utc_time(datetime_str):
      """
      Handles datetime argument conversion to the GNIP API format, which is
      `YYYYMMDDHHSS`. Flexible passing of date formats in the following types::
  
          - YYYYmmDDHHMM
          - YYYY-mm-DD
          - YYYY-mm-DD HH:MM
          - YYYY-mm-DDTHH:MM
  
      Args:
          datetime_str (str): valid formats are listed above.
  
      Returns:
          string of GNIP API formatted date.
  
      Example:
          >>> from searchtweets.utils import convert_utc_time
          >>> convert_utc_time("201708020000")
          '201708020000'
          >>> convert_utc_time("2017-08-02")
          '201708020000'
          >>> convert_utc_time("2017-08-02 00:00")
          '201708020000'
          >>> convert_utc_time("2017-08-02T00:00")
          '201708020000'
      """
      if not datetime_str:
          return None
      if not set(['-', ':']) & set(datetime_str):
          _date = datetime.datetime.strptime(datetime_str, "%Y%m%d%H%M")
      else:
          try:
              if "T" in datetime_str:
                  # command line with 'T'
                  datetime_str = datetime_str.replace('T', ' ')
              _date = datetime.datetime.strptime(datetime_str, "%Y-%m-%d %H:%M")
          except ValueError:
              _date = datetime.datetime.strptime(datetime_str, "%Y-%m-%d")
      return _date.strftime("%Y%m%d%H%M")